import java.util.Scanner;

public class DAY6 {
    public int StrToInt(String str) {
        char[] ch=str.toCharArray();
        if(str.isEmpty()){
            return 0;
        }
        int s=1;
        if(ch[0]=='-'){
            s=-1;
            ch[0]='0';
        } else if (ch[0]=='+') {
            s=1;
            ch[0]='0';
        }
        int sum=0;
        for (int i = 0; i < ch.length; ++i) {
            if(ch[i]<'0'||ch[i]>'9'){
                sum=0;
                break;
            }
            sum=sum*10+ch[i]-'0';
        }
        return sum*s;
    }
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int col = in.nextInt();
        int row= in.nextInt();
        int count=0;
        int[][] array=new int[col][row];
        for (int i = 0; i < col; i++) {
            for (int j = 0; j < row; j++) {
                if(array[i][j]==0){
                    count++;
                    if(i+2<col){
                        array[i+2][j]=1;
                    }
                    if(j+2<row){
                        array[i][j+2]=1;
                    }
                }
            }
        }
        System.out.println(count);
    }
}
